Re: [Intel-gfx] [PATCH v7 0/9] dyndbg: drm.debug adaptation

jim.cromie
2022-10-27T15:38:24Z

On Thu, Oct 27, 2022 at 9:08 AM Jason Baron <jbaron@akamai.com> wrote:
>
>
>
> On 10/21/22 05:18, Jani Nikula wrote:
> > On Thu, 20 Oct 2022, Ville Syrjälä <ville.syrjala@linux.intel.com> wrote:
> >> On Sat, Sep 24, 2022 at 03:02:34PM +0200, Greg KH wrote:
> >>> On Sun, Sep 11, 2022 at 11:28:43PM -0600, Jim Cromie wrote:
> >>>> hi Greg, Dan, Jason, DRM-folk,
> >>>>
> >>>> heres follow-up to V6:
> >>>> rebased on driver-core/driver-core-next for -v6 applied bits (thanks)
> >>>> rework drm_debug_enabled{_raw,_instrumented,} per Dan.
> >>>>
> >>>> It excludes:
> >>>> nouveau parts (immature)
> >>>> tracefs parts (I missed --to=Steve on v6)
> >>>> split _ddebug_site and de-duplicate experiment (way unready)
> >>>>
> >>>> IOW, its the remaining commits of V6 on which Dan gave his Reviewed-by.
> >>>>
> >>>> If these are good to apply, I'll rebase and repost the rest separately.
> >>>
> >>> All now queued up, thanks.
> >>
> >> This stuff broke i915 debugs. When I first load i915 no debug prints are
> >> produced. If I then go fiddle around in /sys/module/drm/parameters/debug
> >> the debug prints start to suddenly work.
> >
> > Wait what? I always assumed the default behaviour would stay the same,
> > which is usually how we roll. It's a regression in my books. We've got a
> > CI farm that's not very helpful in terms of dmesg logging right now
> > because of this.
> >
> > BR,
> > Jani.
> >
> >
>
> That doesn't sound good - so you are saying that prior to this change some
> of the drm debugs were default enabled. But now you have to manually enable
> them?
>
> Thanks,
>
> -Jason

Im just seeing this now.
Any new details ?

I didnt knowingly change something, but since its apparently happening,
heres a 1st WAG at a possible cause

commit ccc2b496324c13e917ef05f563626f4e7826bef1
Author: Jim Cromie <jim.cromie@gmail.com>
Date: Sun Sep 11 23:28:51 2022 -0600

drm_print: prefer bare printk KERN_DEBUG on generic fn

drm_print.c calls pr_debug() just once, from __drm_printfn_debug(),
which is a generic/service fn. The callsite is compile-time enabled
by DEBUG in both DYNAMIC_DEBUG=y/n builds.

For dyndbg builds, reverting this callsite back to bare printk is
correcting a few anti-features:

1- callsite is generic, serves multiple drm users.
it is soft-wired on currently by #define DEBUG
could accidentally: #> echo -p > /proc/dynamic_debug/control

2- optional "decorations" by dyndbg are unhelpful/misleading here,
they describe only the generic site, not end users

IOW, 1,2 are unhelpful at best, and possibly confusing.

reverting yields a nominal data and text shrink:

text data bss dec hex filename
462583 36604 54592 553779 87333 /kernel/drivers/gpu/drm/drm.ko
462515 36532 54592 553639 872a7 -dirty/kernel/drivers/gpu/drm/drm.ko

Signed-off-by: Jim Cromie <jim.cromie@gmail.com>
Link: https://lore.kernel.org/r/20220912052852.1123868-9-jim.cromie@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>